CF8M vs SS316: Difference Between Cast and Wrought 316 Stainless Steel

Is CF8M the same as SS316? No. CF8M is the cast form of 316 stainless steel, and SS316 is the wrought form made as bar, plate, pipe or forgings. Both contain 2 to 3% molybdenum and resist chlorides equally well. CF8M has more chromium, less nickel and 5 to 20% ferrite, which makes it slightly magnetic and easier to cast into complex shapes.

If a drawing says "SS316" on a valve body or pump housing, the part will almost certainly be made as a casting, and the foundry will pour CF8M. Knowing why the two grades differ helps you write the right specification, read the mill certificate correctly, and avoid rejecting good parts because a magnet sticks to them.

This guide compares CF8M and 316 on chemistry, microstructure, strength, corrosion, welding, standards and, cost. It ends with a simple rule for choosing a casting or a machined part.

CF8M vs SS316 at a glance

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What is the difference in chemical composition between CF8M and 316?

The two grades carry the same molybdenum and carbon limits, but CF8M shifts chromium up and nickel down. The foundry needs that balance to produce ferrite during solidification.

Balance iron. The higher silicon allowance is why cast and wrought specifications are written separately. Silicon helps molten metal fill the fine detail of a ceramic shell, but it is not wanted in rolled plate.

Why is CF8M magnetic when 316 is not?

CF8M is slightly magnetic because its cast structure holds 5 to 20% delta ferrite, a magnetic phase. Annealed wrought 316 is fully austenitic and barely responds to a magnet.

Ferrite forms as the casting solidifies. In wrought 316, rolling and annealing remove it. In a casting there is no rolling, so the chemistry is set to keep a controlled amount on purpose. That ferrite brings three benefits:

• Fewer hot cracks. Ferrite absorbs impurities that would otherwise crack the casting as it cools.
• Better weld repair. Ferrite reduces cracking when a foundry repair-welds a casting.
• Higher resistance to chloride stress corrosion cracking than a fully austenitic structure.

There is one limit. Long service between about 300°C and 500°C can slowly reduce the toughness of the ferrite, known as thermal ageing. For most valve and pump service this never applies.

Buyer tip: a light pull on a magnet does not mean the wrong alloy. To confirm the grade, check the mill test certificate, or ask for a PMI (positive material identification) scan by XRF. If the magnetic response matters, specify a ferrite range on the order. Our CF8M material guide explains the ACI naming system and ferrite control in more detail.

Is CF8M stronger than 316?

On paper, wrought 316 has a higher minimum tensile strength and elongation, and both grades share the same minimum yield strength. In real parts the gap is small, because properly annealed CF8M usually tests well above its minimums.

On heat lots solution annealed in Precimetal's in-house solution annealing furnace, CF8M tensile results of 520 to 560 MPa and elongation above 40% are normal.

Wrought 316 has a finer, more uniform grain after rolling, which explains its higher ductility minimum. Designers rarely size a valve body or pump casing on that difference. Both grades sit in the same pressure-temperature group (Material Group 2.2) in ASME B16.34, so a CF8M valve body and a forged F316 valve body carry the same pressure ratings.

Does CF8M have the same corrosion resistance as 316?

Yes, for most service. Corrosion resistance in these grades comes mainly from chromium and molybdenum, and CF8M matches 316 on molybdenum while carrying more chromium. Both handle seawater, brackish water, chlorides and many process acids far better than 304 or CF8.

Two things decide whether a CF8M casting actually performs like 316:

1. Solution annealing. ASTM A351 requires heating to 1040°C (1900°F) minimum and a rapid quench. A skipped or slow quench leaves chromium carbides at grain boundaries, which causes intergranular corrosion.
2. Surface condition. Iron picked up from shot blasting or handling can rust on the surface. Pickling and passivation remove it.

For corrosion-critical parts, ask for an ASTM A262 Practice E intergranular corrosion test on the first article. For sour service with H₂S, see our NACE MR0175 guide for the extra hardness and heat-treatment limits.

Can CF8M be welded to 316?

Yes. CF8M welds readily to wrought 316 or 316L using ER316L or ER316LSi filler. Its ferrite content actually makes it less prone to hot cracking than fully austenitic 316.

If the joint will not be re-annealed after welding, specify the low-carbon cast grade CF3M, matched with 316L pipe. Many foundries pour CF8M with carbon below 0.03% so a single heat can be dual-certified to CF8M and CF3M. Ask for this on welded valve-and-pipe assemblies.

CF8M and 316 equivalent grades and standards

CF8M and 316 have different numbers in every standard system, because each system lists cast and wrought grades separately. Use the cast column for castings and the wrought column for everything else.

A common error online lists CF8M under UNS S31600. That number belongs to wrought 316 only. CF8M is UNS J92900.

For European projects under the Pressure Equipment Directive, ask whether the foundry can dual-certify a heat to CF8M and EN 1.4408. Precimetal holds PED 2014/68/EU certification and can certify to both when the chemistry sits in the overlap.

When should you choose a CF8M casting instead of machining 316?

Choose a CF8M investment casting when the part has complex geometry and is needed in repeat quantities. Choose 316 bar, plate or forging when the shape is simple or you need only a few pieces.

Why casting often costs less: 316 bar is expensive, and machining a valve body from solid can turn more than half of it into chips. Investment casting produces a near-net shape, so machining is limited to sealing faces, bores and threads. The wax-pattern die is a one-time cost spread across the production run.

Why bar can cost less: for low quantities, the die cost per piece is too high, and a CNC shop can start from stock bar the same week.

For a worked cost comparison, read CF8M investment castings: when to choose cast 316.

How to specify CF8M or 316 on a drawing

Write the cast grade and its specification on any drawing for a casting, not "SS316". A vague callout lets each supplier interpret it differently and makes incoming inspection harder.

Also state on the purchase order:

• Certificate type, usually EN 10204 3.1
• Heat treatment chart with the certificate
• Extra tests: radiography, dye penetrant, hydrotest, A262 Practice E, ferrite range
• Surface finish, pickling and passivation
• Dimensional tolerance class; see our guide to investment casting tolerances

Where CF8M and 316 are used

CF8M dominates fluid handling: valve bodies, bonnets and discs, pump casings and impellers, and pipe fittings for water treatment, chemical plants, marine and oil and gas service. Wrought 316 is used for the shafts, stems, fasteners, tube and plate that sit alongside those castings. In general engineering, CF8M brackets and housings replace fabricated 316 assemblies in coastal and washdown environments.

Frequently asked questions

Is CF8M the same as SS316?

CF8M is the cast equivalent of SS316, not an identical alloy. Both contain 2–3% molybdenum and have similar corrosion resistance. CF8M has higher chromium, lower nickel and some ferrite, and it is specified under ASTM A351 or A743 instead of A240 or A276.

What is CF8M equivalent to?

CF8M is equivalent to wrought AISI 316 stainless steel. Its other designations are UNS J92900, EN 1.4408 (GX5CrNiMo19-11-2) and JIS SCS14.

Is CF8M magnetic?

Yes, slightly. Its 5–20% delta ferrite gives a weak magnetic pull. This is normal for cast 316 and does not mean the material is wrong.

Which is better, CF8M or 316?

Neither is better overall; each suits a different product form. Use CF8M for cast parts with complex shapes, such as valve bodies and pump casings. Use 316 for bar, plate, pipe and simple machined parts.

Is CF8M the same as 316L?

No. The cast equivalent of 316L is CF3M, with carbon limited to 0.03%. CF8M allows 0.08% carbon, like standard 316.

What is the difference between CF8M and CF8?

CF8M contains 2–3% molybdenum and CF8 contains none. CF8 is cast 304 and CF8M is cast 316, so CF8M resists chlorides and seawater much better.

Why is CF8M used for valve bodies?

Valve bodies have complex internal passages that are expensive to machine from solid. CF8M casts these shapes close to final size, resists corrosion like 316, and is listed in ASME B16.34 for pressure service.

Conclusion: CF8M or 316?

CF8M and 316 are the same corrosion-resistant alloy family in two product forms. CF8M is the right callout for any cast part, and 316 is the right callout for bar, plate, pipe and forgings. The chemistry differences, the ferrite and the slight magnetism exist because CF8M is designed to be cast. They are not signs of a weaker material.

The decisions that protect your part sit on the drawing. Name the cast grade and its ASTM or EN specification, require solution annealing, and ask for the tests your service needs.

Get a quote for CF8M castings

Precimetal Cast has poured CF8M, CF3M, CF8 and CF3 in Kadi, Gujarat, since 2001. Every heat is solution annealed in-house, inspected on CMM, and machined to drawing when required. Our plant is IATF 16949:2016 and ISO 9001 certified, holds PED 2014/68/EU certification, and exports to more than 15 countries.

Send your drawing for a free quote and get material confirmation, tooling and per-piece pricing, and lead time within 48 hours. Drawings are kept confidential, and we sign NDAs on request.

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